1. Field of the Invention
The present invention relates generally to a method and apparatus for casting concrete members, and more particularly to a method and apparatus for casting multiple-slab, hollow-core concrete members having structural tying members extending between the slabs.
2. Discussion of the Prior Art
In casting some concrete members, it is advantageous to use molten wax cooled to a solid state as the bottom of the mold or form. For example, concrete panels having embedded decorative or functional elements in one surface can be advantageously formed using a wax mold bottom, as shown in Terrio U.S. Pat. No. 3,331,175. However, until recent years, those in the art had not been able to develop techniques which permitted easy removal of all of the wax from the cast slab and casting bed after the concrete had cured. One of the first successful attempts is disclosed in U.S. Pat. No. 3,608,051. This patent teaches a method in which hot water or steam is directed around the mold members and into direct contact with exposed peripheral edges of the wax layer to melt the wax and thus remove it from the slab and mold. This was an improvement over earlier proposals in that the wax is substantially completely removed and can be separated from the hot water for reuse.
A variation of this technique is disclosed in U.S. Pat. No. 3,689,626 for casting multiple-slab, hollow-core concrete panels. In this method, wax is used to cast concrete members having two or more spaced apart slabs with structural steel tying members joining them together. In the method of this patent, a first layer of wet concrete is poured into a mold formed within an enclosed water-tight tank. The concrete is poured onto a mold bottom formed by a layer of solidified wax at least partially supported by a pool of water below the wax layer. Upwardly extending tying members are embedded in the wet concrete and a second layer of water is introduced into the tank. Molten wax is introduced into the tank to cover the water and to form, when solidified, a second mold bottom spaced above the first slab. Cold water is circulated below the wax layer to cool and solidify the wax to form the second mold bottom. The height of the wax layer is such that the tying members extend above. When the wax has solidified, a second layer of wet concrete is poured onto the suspended wax layer to cover the upper ends of the tying members and form the second slab. When this upper layer of concrete has set sufficiently to be self-sustaining, the cold water in the tank is displaced by hot water, and hot water is circulated through the tank until all of the wax is melted and removed through an appropriate tube.
The method just described is a great improvement over prior methods of forming multiple slab hollow panels. The system depends, however, on the construction of a large water-tight tank with suitable casting deck forming the bottom of the tank or construction within the tank. All form work for the concrete structures to be made therein are independent of the tank and deck structure. Thus, any size or shape of panel could be formed so long as it did not exceed the area limits of the casting deck. When the product to be made required the embedding of decorative materials, a reticulated structure was placed within the tank to serve as a casting deck. Since the perimeter forms for containing concrete were inside the tank perimeter, it was necessary to use a cover over the entire surface of the tank during the curing operations in order to prevent undue heat loss.
While such method provides great flexibility in terms of the variety of products which can be produced, the system does not lend itself to portability. The whole system is larger and more cumbersome than required to make quantities of products having predetermined dimensions.
Hence, it is a primary object of the present invention to provide a method, apparatus, and system for casting concrete members which are improvements over those disclosed in U.S. Pat. No. 3,689,626, and which effectively and reliably overcome the drawbacks and limitations of the prior art proposals. More specifically, the present invention has as its objects one or more of the following taken individually or in combination.
(1) To provide a self-contained, portable system for casting concrete members;
(2) The provision of self-contained wax and water distribution channels and drainage channels in a system for casting concrete members;
(3) To provide means for simply and accurately controlling water level in a concrete casting system for casting multiple slab castings with structural members extending therebetween;
(4) The development of valve means which expedites removal of wax from a concrete casting mold;
(5) To provide a method and system for casting multiple-slab, hollow-core concrete panels on any flat bed without the need for a special water-tight tank in which to place the mold;
(6) To provide a method and system for casting multiple-layer, hollow-core concrete panels which can be utilized efficiently at a job site;
(7) To provide a method and system for casting multiple-layer concrete panels in which the perimeter forms for the finished product combine with the deck on which they are placed to form the container necessary for containment of liquids required in the process;
(8) To provide a method and system for casting multiple-layer concrete panels without the need for a structural cover during curing operations; and
(9) To develop a casting system which is versatile in that it can be easily modified to cast panels of a wide variety of dimensions.